The recent diseases of Vannamei shrimp like, Infectious Myonecrosis Virus (IMNV), Early Mortality Syndrome (EMS) and White Feces Syndrome (Enterocytozoon hepatopenaei?EHP? have severe impact on the shrimp farming industry, especially in Asian continent. The shrimp technicians and farmers have modified and improved the existing techniques in hatchery, water disinfection, and sanitation and in culture practices. More emphasis has been given on the pathogen free and biosecured live feed to shrimp broodstock and post larvae. The culture ponds are supplied with pathogen free larvae and cleaned water for secured shrimp production. The article is giving in lights on the different aspects of biosecured and disease-free farming system.
- Maturation and Hatchery Biosecurity system
Pathogen free broodstock is generally imported from non-shrimp farming region. The pathogen like EHP and Vibrio species including Vibrio parahemolyticus EMS strain (VPEMS) have been proven to be transmitted or carried by Polychaete and Artemia. The procurement of these live food should be done from biosecured region.
The Post Larvae culture should be done in biosecured culture environment. The efforts should be made to reduce the density of pathogen Vibrio in natural food like algae and live food like artemia. The PL should be screened by the advanced techniques, like qPCR for pathogen presence.
The water disinfection in hatchery is generally performed by filtration system as chemicals are harmful for the larvae. The gravity filtration system, Ozone Disinfection, UV-Disinfection and Ultrafiltration system are commonly practiced.
- Water Disinfection in Shrimp Culture Ponds
The modern shrimp farms use reservoir for water storage and disinfection. The sedimentation, elimination of carrier/vector of potential pathogen by chemical application, chemical uses for free pathogen degeneration have been practiced. It has been observed that the elimination of pathogen bacteria, like Vibrio is not possible. The efforts should be done to minimize the load the pathogenic bacteria in the culture environment by means of probiotics or herbal supplements. Presence of almost no residue in the animal due to the uses is the advantage of probiotics and herbal supplements.
- Culture pond preparation
The pond bottom should be cleaned properly to make sure there is no pathogen carriers and no pathogen like EHP, are present. There are several types of pond bottoms, like, earthen, concrete and HDPE lined ponds. All have their own advantages and disadvantages.
- Adapted Culture Methods
There is continuous advancement and improvement in shrimp breeding, PL rearing and grow out culture methods. The improvements and adaptive changes in the culture methods are mainly due to change in environment, characteristics of pathogens and production requirements and above all is market demands. Some of the adaptive and advancement culture methods of shrimp farming are described in short below,
- In-house technique to control temperature and plankton bloom: This culture practice is quite established and popular in China. This technique became more popular after EMS and later white feces syndrome. The characteristics of closed recirculation system and no contact with outside environment and no fluctuation of plankton and other water quality parameters makes it free from pathogen and shrimp mortality. The farmers with huge investment usually go for high stocking density. The shrimp are usually sold live in domestic market.
- Vannamei Mixed culture or Polyculture: Polyculture technique (Fish with White shrimp) has become popular in Eastern and Southern China. The commonly used fish is Tilapia. Apart from Tilapia, other fish like, milk fish, sea bass also are practiced. The Vannamei is stocked at PL 10 with 60,000 pieces/Mu and after a week Tilapia 250 pcs/Mu are stocked. The stocking size of Tilapia is 2.5 -3 cm. The harvesting size of shrimp is 10 g whereas Fish 700-800 g. Only Tilapia feed is provided and shrimp are allowed to feed naturally. The Survival rate of Tilapia reaches up to 95% whereas of Shrimp 50%.By contrast, the polyculture ponds have less disease than the monoculture ponds. This method is mainly practiced in low salinity water area. The low salinity and presence of fish is able to reduce the pathogen like, Vibrio and other bacteria in the culture water.
- Two step shrimp culture: This method started in the SE-Asian region after EMS outbreak. The first step is nursery culture in which PL 10 is raised up to 0.5 g to 1 g of weight prior releasing to the culture ponds. The main purpose is to secure the animals to be not get infected by EMS bacteria. The two-step culture practice has been quite successful in having EMS-free shrimp. Beside it, the two-step farming also improved the total shrimp productivity by increasing the number of crops and so the profitability of the farmer.
- Plankton free shrimp culture: The growth of plankton is discouraged in this culture system. The concept is to provide the shrimp stress free culture environment. The density of plankton is kept at as low as possible so its fluctuation will not have major impact on the critical water quality parameters and so on the shrimp living. This concept is called under various names, like, Muatan system, Colloid system and Aquamimicry etc. in various region of SE-Asia. This system has been able to reduce the incidences of EMS and of EHP up to some extent.
The improvement in the existing culture system is related to investment. Any investments need a proper and profitable business model. The recent improvements in farm infrastructure and culture practices are mainly done to have disease-free and quality shrimp production. The improved culture techniques also improved the quality of shrimp-like, live fresh sale with higher price, darker color shrimp have enhanced the selling price of the shrimp and so the profitability.
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